Metallurgical process.



UNITED, STATEs PATENT OFFICE.

EDWARD coonmon AOHESON, or BUFFALO, NEW YORK.

M ETAILLU'RGICAI. PROCESS.

SPECIFICATION forming part of Letters Patent N 0. 693,482, datedFebruary .18,- 1902.

Application 1119a Octobe 1'14, 1899. Serial No. 733,635. (NospecimenslTo all whom it may concern:

Be it ,known that I, EDWARD GOODRICH ACHESON, a citizen of the UnitedStates, residing at Buffalo, in the county of Erie, State of New York,have invented certain new and useful Improvements in MetallurgicalProcesses, of which the following is a specification.

. My invention relates to metallurgical proc esses, and moreparticularly those for the production of pure metals, carbids, and otherchemical compounds that are produced in an electric furnace in whichcarbon is used as a conducting, reducing, or combining agent; and it hasfor its object to provide a process or method of cheaply and practicallyproducing pure [metals, carbid s, alloys, and other chemical compoundsand products,and it may be said to consist, generally stated, in the useof. graphite as a conducting, reducing, or combining agent whenassociated with the metallic ore to be reduced or other substances orcompounds to be operated upon.

Efforts heretofore made for the practical direct production of pureproducts in an electric furnace--as, for example, metals like siliconorfor the production of pure compoundsas, for example, carbids ofcalcium-have proved failures, owing, among otherthings, to difficulty ineffecting the reduction and also to the introduction into the finishedproduct of impurities contained in the carbon used as a conducting,reducing, or combining agent, or to carbon itself, resulting in theformation of impure products. I have discovered that the abovedifficulties attending the reducing action in the electric furnace canbe overcome and greatly improved results obtained by using asconducting, combining, and reducing agentgraphite, and preferablygraphite which has been produced by the electric furnace. In thisprocess I utilize not only the purity and high electrical and thermalconductivity of graphite, but I have discovered that its softness anddivisibility give it a peculiar property of being brought to anextremely effective distribution with the ore or other substance to beoperated upon. ductivity facilitates the passage of sufficient currentto produce the desired reactions. Its high thermal conductivityfacilitates the con- Its high electrical con'-' I duction of heatthroughout the mass of ore or othersubstances with which it is mixed,and its softness and divisibility facilitate its distribution throughoutthe mass of ore or other substance with which it is mixed and permitthe. fullest utilization of the graphiteas an electrical andthermal-conductor and reducing agent.

I have found that when an ore such as granulated silica andamorphouscarbon in an amount sufficient for the reduction of such oreare mixedin the mannerand tothe extentordinarily practiced in making amixture of said materials the mixture is practically non-conductive forcurrents as ordinarily used for metallurgical work, and even after .aprolonged or thorough mixture its electrical conductivityis notsufficiently high for practical operation in the process of electricalreduction of the ore. When, however, graphite is substituted for theamorphous carbon, owing to its high conductivity, softness, anddivisibility it can be so mixed with the ore or other material as tofurnish the proper and desired degree of electric conductivity, andowing to the softness and divisibility'of the graphite during theprocess of mixing it with the granulated ore the particles of ore becomewholly or partially coated with the graphite, and good electrical conductivityis established throughout the mass with all the particlesthereof by reason of this surface coatingof the particles of the ore. Inorder to get this partial or complete coating of the particles of ablyaccomplished by a tumbling or rubbing process, and the increase ofconductivity and successful resultant reducing operation depend largelyupon the thoroughness with which the graphite is coated or spread uponthe surface of the particles of ore. Thus even when the particles of oreare mixed with graphite in the manner and to the extent or-.

dinarily practiced in making a mixture I have found that the electricalresistance is excessively high, so as to practically inhibit the use ofthe electric current in reducing the ore, but on continuing the mixingand rubbing process, so that the particles of orejbecome partially orwholly coated with the graphite, the electrical resistance of the massis reduced until its conductivity is so far increased as to permit ofthe successful operation of the reduction with electric currents asordinarily used in electrometallurgical processes. For the applicationof myinvention I reduce the ore and graphite to particles, preferably tosmall particles or powder, placing the desired amount of each in asuitable tumbling barrel or mixer and mixing the same, thus to a greateror less extent coating or varnishing the ore particles with the softgraphite. The mixture of ore and graphite is then introduced into anelectric furnace, where it is subjected to a temperature sufficient tocause the desired reactions-as, for instance, the reduction of the oreand the liberation of the metal. \Vhile any kind of suitable furnace maybe used, a direct-acting furnace, wherein the charge to be operated uponis placed or caused to pass directly between the electrodes and in whichthe current passes through the charge, is more desirable.

Graphite made in the electric furnace-has the advantage of great purity,sometimes containing as low as 0.033 per centum of ash, having thecapacity, owing to its soft nature and divisibility, of being broughtinto very intimate contact with the ore and also possessing extremelyhigh electric and thermal conductivity, having usually more than twicethe conductivity of the best conducting amorphous carbon. Highelectrical conductivity is of first importance--for example, when themetal on being freed from the ore combines with any free carbon or otherelement present to form carbids, alloys, or impure metal and it isdesired to obtain a pure metal-for instance, in reducing silica for theproduction of pure silicon. In making pure elementary substancessuch,for example, as siliconby direct reduction it is essential that thecontents of the furnace consist solely of the pure ore or silica andcarbon in an amount not greater than necessary for the reduction. Such amixture of silica and carbon in the amorphous condition is an extremelypoor conductor of electricity, and for this reason it is impracticableto make pure silicon when the amorphous carbon is used. When graphite,however, is used for this purpose and is mixed with the silica in a likeamount and in the manner above indicated, I have discovered that a goodconductivity is obtained and a successful and practicable op eration canbe performed.

A good illustration of the value and application of my invention is inthe reduction of those ores, such as silica and alumina, which aredifficult of reduction and from which it has not been heretoforepracticable to extract the metal directly in a pure state.

All four of the qualities belonging to graphite and abovementionedpurity, electrical conductivity, thermal conductivity, andcapacity of coating or being spread over the surface of the particleswith which it is brought in contact-are of great value. Pu-

rity is essential, as it is well known that the presence of a very smallpercentage of other elements will frequently make metals worthless.Oapacity for intimate mixture and coating of the ore to be reduced is ofgreat importance, as is also high electrical conductivity of thereducing-carbon, for on it must be placed the burden of conducting theelectric current, and usually an excess of this carbon over thatnecessary for the reduction is not permissible, as a carbid of the metalwould be produced or the excess of carbon would enter as an impurity inthe metal. High thermal conductivity is desirable, as it facilitates thedistribution of the heat throughout the mass of the charge where thereis a tendency to its local generation, as would occur where the currentfound a path of least resistance.

As one example of the application of my invention I will describe thereduction of silica and extraction of pure silicon. I takeelectrically-made graphite and pure silica both in a state of finepowder and mix them in the proportion of graphite fifty-five parts andsilica one hundred and fifty parts. The theoretical proportion would begraphite fiftyfive parts and silica 137.5 parts; but I prefer to have alittle less than the theoretical amountofcarbon. The mixture isthoroughly rubbed together in a mortar, tumbling-barrel, or othersuitable device. The amount and perfection of the intermingling andrubbing has much to do with the efficiency of the operation and with theelectromotive force necessary to employ for passing the electric currentthrough the mass when in the electric furnace, and it should be welldone. The material thus prepared is placed in an electric furnace insuch manner that the current passing from electrode to electrode willpass through it, and around the charge on the bottom, side, and top isplaced fine silica as a support and covering to the mixture and liningto the furnace, which may be made of brick or other suitable material.The mixture having been placed in this manner in its envelop of silicaand in direct contact with the opposing electrodes the current is causedto pass in sufficient volume and for suflicient time to produce thereduction of the silica and liberation of the silicon. Thus in anoperation which I have conducted with the electrodes separated to adistance of three inches and each having an exposed end surface of foursquare inches, the intervening space measuring three inches by twoinches by two inches, with its floor and sides of silica, was filledwith the mixture of graphite and silica above described, and over allwas placed a layer of silica. The current was turned on with one hundredvolts. At the beginning the current registered three amperes, butquickly rose and after seven minutes registered eighteen amperes. Thecurrent was turned off after twenty-five minutes, the maximum voltagehaving been one hundred with \Vhen the product of the operation is aVela twenty amperes. Carbon monoxid gas escaped freely and burned on thesurface. opening the furnace a partof the silicon resulting from thesilica of the charge is found as'globules of pure silicon mingled withother portions of the charge not Wholly reduced. These globules may beseparated from the unreduced mass by floating in water or otherdesirable method.

It is evident that various forms of furnaces may be used in carrying outmy invention and that the product may be removed in many ways. Thus itmay be removed intermittently either in a fluid or vsolid condition, asis the practice in making car-horundum, carbid of calcium, andaluminiumcontinuously either in a solid, liquid, or gaseous state.

tile metal and can be removed from the furnace in a gaseous condition,as in the reduction of zinc and other metals, suitablecondensing-chambers are provided for its reception and retention.

When alloys are to be made of two or more metals, one or more of themetals may be mixed in the powdered metallic state with the ore to bereduced, or the ores of the several metals may be mixed With theappropriate amount of graphite to produce their united reduction,and'the metals when liberated Will alloy together. Thus oxid of iron andsilica in the proportions necessaryforthe production of the desiredsilicid of iron, when mixed with the necessary graphite and raised tothe proper temperature, will be reduced to a silicid of iron. Whencarbids are to be made, the amount of graphite employed in the charge isincreased over and above that necessary for the reduction to at leastthe extent of the amount necessary to combine with the metal and formthe desired carbid.

I claim I v p 1. The method herein described of reducing ores, whichconsists in mixing pulverized ore with graphite as the sole conductingand reducing agent, both in a dry state, coating the particles of orewith graphite, and passing an electric current through the mass of suchcoated particles, thereby heating it to a point sufficient to effectreduction of the ore.

2. The method herein described of reducing ores, which consists inmixing pulverizedore withsufficient graphitic carbon as the soleconducting and reducing agent, toreduce the ore, both in a dry state,coating the particles of ore with the graphitic carbon and passing anelectric current through the mass of such coated particles, therebyheating it to apoint sufficient to effect reduction of the ore.

3. The method herein described of reducing ores, which consists inmixing pulverized ore and graphitic carbon in the theoretical proportions necessary for the reduction of the ore, coating or partiallycoating the particles of ore with the graphitic carbon, and passing anelectric current through the mass of such coated particle's, therebyheating it to a point sufficient to effect reduction of the ore.

In testimony whereofI have hereunto set my hand. i Y

EDWARD GOODRICII ACIIESON.

Witnesses:

GEo. B. BLEMMING, O. O. BITTNER,

